Reversibly deformable artificial cornea and methods for implantation

ABSTRACT

An artificial cornea is formed from a hydro gel polymer and includes a monolithic body having a center optic surrounded by an annular rim. Artificial cornea is inserted into a central anterior opening in a cornea so that the annular rim enters an annular pocket surrounding the opening. The height of the center optic matches the depth of the central opening so that the level of the artificial cornea matches that of the native cornea.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. 119 of U.S. Provisional Patent Application No. 61/388,386, filed Sep. 30, 2010, the full disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and methods. More particularly, the present invention relates to the structure of an artificial cornea and methods for inserting the implant into a cornea.

Cornea blindness has been a source of suffering for mankind since pre-historic times and is documented in the Bible. For the last 200 years there have been attempts at synthetic replacements for the cornea (“artificial corneas”). Unfortunately, the vast majority of these attempts have resulted in failure. Common problems with artificial corneas include intraocular infection and extrusion of the implant.

Most artificial corneas have been implanted in a penetrating fashion where the artificial cornea is in direct contact with the aqueous fluid in the eye. Because the synthetic materials which have been used for artificial corneas have not been able to completely integrate with the surrounding corneal tissue, bacteria from the surface of the eye can travel along microscopic openings between the artificial cornea and the circumscribing corneal tissue resulting in intraocular infection (endophthalmitis) which can cause loss of the eye.

Extrusion of artificial corneas can result from any one or more of three primary causes identified by the inventors herein. The first cause is the use of relatively large incisions for implantation. For example, the AlphaCor™ Artificial Cornea from Addition Technology, Inc, requires a 16 mm incision for implantation into an intralamellar pocket. The AlphaCor artificial cornea must be sutured in place with resorbable nylon sutures. The cornea has a vascular tissue and heals poorly. Once the nylon sutures dissolve over a period of several years, the corneal scar tissue may not be sufficient in strength to hold the artificial cornea within the cornea, commonly resulting in extrusion.

A second potential cause of extrusion of artificial corneas is interference with corneal physiology. For example, some artificial corneas have been made from materials that are impermeable to both oxygen and glucose e.g. polymethylmethacrylate. Polymethymethacrylate has effectively no measurable oxygen permeability and therefore has a dK of zero Barrer. Over time the lack of adequate oxygenation and nutrition of the corneal tissues can result in melting of the cornea followed by extrusion.

A third potential cause of extrusion of artificial corneas is excessive rigidity of the artificial cornea. Very stiff materials, such as polymethylmethacrylate which has a Young's modulus between 1800 and 3100 MPa, can erode through the cornea over time. Such erosion can result from blinking of the eyelid which deforms the cornea and can abrade corneal tissue as the tissue repeatedly rubs against the rigid implant material. Such erosion can in turn lead to extrusion.

In addition to these problems, present artificial corneas can be uncomfortable for the patient. For example, the patient's tear film can be disrupted by the implant projecting above or falling below the surface of the surrounding cornea. Projection of the implant above the surface of the cornea can also cause abrasion of the inside of the eyelid. An implant with an optic below the surface of the surrounding cornea can also allow deposition of mucus into the “hole” which can obscure the vision.

For these reasons, it would be desirable to provide improved artificial corneas which overcome at least some of the problems noted above. In particular, it would be desirable to provide artificial corneas and methods for their implantation where the risk of infection of the eye is reduced. It would be further desirable to provide artificial corneas which are resistant to extrusion due to any of the reasons cited above. Additionally, it would be desirable to provide artificial corneas which are comfortable for the patient and which maintain the tear film with minimum disruption. At least some of these objectives will be met by the inventions described below.

2. Description of the Background Art

Corneal implants are described in U.S. Pat. Nos. 4,842,599; 4,865,601; 5,300,116; 5,292,514; 6,106,552; 6,361,560; 6,673,112; and Publ. No. 2002/0055753; and PCT Application WO99/30645. Corneal implants and methods for their implantation into corneal pockets are also described in commonly owned U.S. Pat. No. 7,223,275; U.S. Patent Publs. 2004/0243160; 2006/0173539; US2010/0069915; and PCT Publ. WO 2008/055118, the full disclosures of which are incorporated herein by reference.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes at least some of the problems noted above with prior artificial corneas. The artificial corneas of the present invention are made to be implanted within the lamellae of the cornea without penetration into the anterior chamber of the eye. By avoiding such penetration, the risk of eye infection (endophthalmitis) is greatly reduced. Moreover, the artificial corneas of the present invention are designed to be sufficiently flexible and durable so that they can be implanted through small incisions into a corneal lamellar pocket when the size of the pocket entry incision is smaller than the artificial cornea. Such implantation is advantageous both because it further inhibits the intrusion of bacteria around the implant into the anterior chamber and because it helps anchor the implant which allows the device to be self-retaining even without sutures or adhesives. Usually, however, the implant will be at least somewhat more rigid than the corneal tissue which will allow the implant to maintain an optically advantageous shape after implantation. Because a typical Young's modulus of the mammalian cornea is between 0.2 and 0.29 MPa, the Young's modulus of the artificial cornea should preferably be greater than 0.29 MPa in order to retain its shape after implantation into the cornea. However, the artificial cornea should not be so stiff as to not be able to bend with the cornea during normal physiologic activities such as blinking. We have determined that the Young's modulus should preferably not be greater than 100 MPa for this to occur with the present invention.

With prior art artificial corneas, it has not been possible to consistently fit the artificial cornea to match the natural shape of the cornea. This is important because a mismatch between the artificial cornea optic and the surface of the cornea causes clinically significant problems. In the case of the Boston Artificial Cornea, elevation of the optic above the level of the carrier donor cornea causes a persistent foreign body sensation for the patient and necessitates the continuous use of a bandage contact lens to prevent abrasion of the conjunctiva on the inside of the eyelid. The optic of the Alphacor on the other hand sits below the level of the host cornea by 300 microns, which creates a divot that continuously accumulates debris such as mucus and thereby limits the visual improvement of the patient. FIG. 7. shows the profiles of prior art artificial corneas and the present invention and how they fit within the host or carrier cornea.

In a specific aspect of the present invention, the artificial cornea is implanted into the cornea using incisions with very precise dimensions. The precision of the dimensions will allow the artificial cornea to fit exactly into the cornea so that the surface of the artificial cornea will be even with the surface of the artificial cornea optic and there will be no gap between the optic and corneal tissue. The ability to create corneal incisions with this high level of precision has only become possible recently with the availability of the femtosecond laser and mechanical corneal pocket makers. In preferred aspects the corneal incisions will be created with a femtosecond laser which commonly has a tolerance of about +/−3 microns. In alternate preferred aspects the corneal pocket incision can also be created with a mechanical corneal pocket maker, which generally will have a tolerance of +/−50 microns or better. A manually made pocket can also be used to implant the artificial cornea of the present invention, however, it would be impossible to assure that the optic would be even with the surface of the host cornea because the human hand is not capable of making incisions with a precision of +/−50 microns.

In preferred aspects, the incisions that create the opening for the optic of the artificial cornea of the present invention will also precisely match the angulation of the optic. i.e. the incision of the cornea which abuts the optic would match the angulation of the optic within +/−30 degrees more preferably +/−10 degrees. For example if the side of the optic creates a 90 degree angle with the plane created by the junction of the rim and the optic, the abutting corneal incision should also be 90 degrees to the plane created by the junction of the rim and the optic.

In alternate preferred aspects, the corneal incisions will be made to excise a volume of corneal tissue having a shape which is similar to the three-dimensional shape of the artificial cornea (FIG. 9A). Such an interference or interlocking fit of the artificial cornea with the corneal tissue can help retain the device within the cornea by as shown in FIG. 9B.

In a specific aspect of the present invention, the artificial cornea has a center optic which will be machined to a very close tolerance to maintain a preselected optic height within a tolerance in the range from ±50 μm or less. As 50 μm is the average thickness of the epithelium over the cornea, and the corneal epithelium will be able to respond by thinning or thickening to offset any difference between the surface level of the artificial cornea and that of the native cornea. Thus, by carefully controlling the depth of the corneal pocket to within a similar tolerance or closer, the optic height of the artificial cornea can be matched with that of the native cornea to preserve the tear film over the eye and artificial cornea and increase patient comfort. The optic height will typically be maintained between 200 μm to 400 μm to allow a sufficient thickness of the natural corneal tissue to cover the rim of the artificial cornea so there is a decreased risk of erosion through tissue. In cases of abnormally thick corneas, such as commonly found in patients suffering from corneal edema due to endothelial failure, the optic height may be as much as 800 microns to compensate for such increased thickness.

Thus, in accordance with the present invention, a reversibly deformable artificial cornea comprises a monolithic body having a center optic surrounded by an annular rim. By “monolithic,” it is meant that the center optic and the rim are a single, continuous body of material free from seams, joints and the like. For example, the artificial cornea may be formed from a single blank or block of material typically a polymeric hydrogel of a type commonly employed in forming intraocular lenses (IOL's), preferably being a copolymer of hydroxyethyl methacrylate and methylmethacraylate, such as C126 commercially available from Contamac Ltd., Essex, U.K. or a hydrophobic acrylic material such as commercially available from Benz Research. The polymeric hydrogel material could also have both hydrophobic and hydrophilic properties, such as a copolymer of hydroxyethyl methacrylate and methylmethacraylate which has undergone plasma surface treatment. Alternatively, the artificial cornea could be molded, machined, or laser cut from a material comprising an interpenetrating network or a collagen-based hydrogel.

The monolithic body, when hydrated, will have a diameter in the range from 4 mm to 10 mm. The center optic will have a diameter in the range from 3 mm to 9 mm and an optic height (D, FIG. 4) in the range from 200 μm to 800 μm. The manufacturing tolerance of the optic height will be +/−50 microns or less, to allow a precise fit to the surrounding recipient corneal tissue. The annular rim will have an annular width in the range of 0.5 mm to 4 5 mm and a median thickness in the range from 50 μm to 200 μm. Preferably the polymeric hydrogel will be selected to have a modulus in the range from 0.3 MPa to 100 MPa when fully hydrated. Preferably tensile strength should be at least 1.5 MPa and the elongation to break should be at least 100%. Suitable body materials should be at least partially permeable to oxygen, typically having an oxygen permeability (dK) of at least 3 Barrer. Exemplary materials with excellent oxygen permeability, e.g. dK of at least 60 include: Lotrafilcon A, Lotrafilcon B, Balafilcon A, Comfilcon A, Senofilcon A, Enfilcon A and Galyfilcon A.

In the exemplary embodiments, the annular rim of the corneal implant circumscribes a posterior edge of the center optic. Further, an anterior surface of the center optic is usually convexly shaped to provide a refractive power generally equal to or consistent with a native cornea, typically being in the range from 30 diopter to 70 diopter, when implanted in the cornea. Usually, the anterior surface of the center optic will be convexly shaped and the posterior surface will be concavely shaped. The radius of curvature of the posterior optic and the rim will typically be consistent with the range of curvature of the native cornea being in a range from 6.2 mm to 10 mm.

In further specific aspects of the present invention, the annular rim will have a plurality of apertures to allow passage nutrients and oxygens therethrough. As the rim will be implanted between adjacent lamellar surfaces of the cornea, it is important that nutrients be able to pass therethrough to maintain health of the corneal tissue. Usually, the apertures will occupy from 10% to 90% of the annular area of the rim, typically occupying about 33% of the area. In the exemplary embodiments the apertures are round holes disposed uniformly about the annular rim, but they could take a number of other geometries such as crenellations in the outer edge of the annular rim.

In a further aspect of the present invention, methods for implanting an artificial cornea in a cornea to replace an impaired center region of the cornea comprise forming a central anterior opening having a posterior surface surrounded by a peripheral sidewall in the cornea. The opening will preferably have a uniform depth, typically in the range from 200 μm to 800 μm, where the depth will be selected to match the height of the peripheral wall of the center optic of the implant, preferably within ±50 μm. The artificial cornea is implanted within the central anterior opening so that the peripheral thickness or wall height of the center optic will match the peripheral sidewall of the central anterior opening to within a tolerance of ±50 μm to provide the advantages discussed above.

In specific embodiments of the method, in addition to forming the central anterior opening, a lamellar pocket will be formed over at least a portion of the peripheral sidewall of the central anterior opening and a rim portion of the implant will be inserted into the lamellar pocket in order to anchor the implant in the opening. Typically, the lamellar pocket will fully circumscribe the central anterior opening and the annular rim will fully extend around the implant. In still further exemplary embodiments the lamellar pocket is formed around the periphery of the posterior surface of the central anterior opening and the annular rim which enters the lamellar pocket is disposed around a posterior edge of the center optic of the corneal implant.

In exemplary embodiments, the central anterior opening is formed to have a diameter smaller than that of the center optic, typically from 70% to 99% of the center optic diameter, so that the partially elastic corneal tissue can seal closely around the peripheral wall of the implant to help prevent extrusion of the implant after sutures are removed, to inhibit ingrowth of epithelial cells, inhibit the entry of bacteria, and prevent loss of fluid from the anterior chamber. The artificial cornea may be implanted within the central anterior opening by one of two different techniques. In the first technique, the artificial cornea is constrained to reduce its width and introduced through an upper surface of the anterior central opening in a posterior direction. The artificial cornea can be released from constraint within the central anterior opening so that it assumes its unconstrained geometry to occupy the volume of the central opening, usually with the annular rim inserting into the lamellar pocket. Alternatively, a separate lateral opening can be formed from the side of the eye into the central anterior opening and the constrained artificial cornea introduced therethrough.

In a particular embodiment, the artificial cornea of the present invention will be adapted to support growth of a viable corneal epithelium over the periphery of the anterior face of the optic. Establishing a viable epithelium over the peripheral anterior surface will advantageously provide a biological seal around the edge of the anterior face of the optic to prevent bacteria from entering the corneal pocket through the junction of the raised optic and the cornea stroma. Preferably, the center of the optic will remain free of corneal epithelium after implantation which will allows the central surface of the optic principal (which is critical to the optical performance) to remain optically smooth even when the patient's eye is not able to form a smooth optically good epithelium. In preferred embodiments, the patient's corneal epithelium will be able to grow onto the periphery of the anterior face of the optic over a width in the range from 0.1 mm to 1 mm.

Promoting the growth of a viable corneal epithelium over the periphery of the anterior optic may be achieved by coating or covalently bonding certain biological molecules which promote such growth, such as extracellular matrix proteins or growth factors, over the periphery of the anterior face of the optic, usually to a width in the range set forth above. Suitable biological molecules include collagen, fibronectin, laminin, fibronectin adhesion-promoting peptide sequence (H-trp-gln-pro-pro-arg-ala-arg-ile-OH) (FAP), and epidermal growth factor. In other preferred aspects the periphery of the optic can be made porous or roughened in texture to allow corneal epithelial cells to bind more easily to the surface of the periphery of the anterior optic face.

Many materials which could be used for the manufacture of the artificial cornea will generally not support the growth of corneal epithelial cells without special surface treatment as described above. In such cases, the artificial cornea can be formed of such a non-growth-promoting material with the periphery treated to promote growth. In the case of an artificial cornea formed from a material that does inherently support epithelial growth, such as collagen or a collagen derivative, a polymer that will not support the growth of epithelium e.g. a silicone or a methacrylate, may be coated over the central optic surface to keep the central optic surface free of epithelium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an artificial cornea constructed in accordance with the principals of the present invention.

FIG. 2 is a top view of the artificial cornea of FIG. 1.

FIG. 3 is a cross-sectional view of the artificial cornea of FIGS. 1 and 2 taken along line 3-3 of FIG. 2.

FIGS. 4 and 5 illustrate the locations of the dimensions set forth in Table 1 hereinafter.

FIGS. 6A through 6F illustrate implantation of the artificial cornea of FIGS. 1-3 into a corneal pocket.

FIGS. 7A through 7C compare the implantation profiles of two prior art artificial corneas with that of the present invention.

FIGS. 8A through 8D illustrate exemplary rim designs for the artificial cornea of the present invention.

FIG. 9A illustrates that a volume of tissue has been removed from the cornea.

FIG. 9B illustrates a corneal implant that is designed to match the volume of the removed tissue shown in FIG. 9A

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-3, an artificial cornea 10 in accordance with the principles of the present invention comprises a center optic 12 surrounded by an annular rim 14. A plurality of apertures 16, typically circular holes, are formed fully through the annular rim to allow the passage of nutrients therethrough after implantation. As illustrated, the apertures 16 comprise about 33% of the total area of the annular rim 14, but the total open or void area provided by the apertures could be anywhere in the range from 10% to 90% of the total area.

The artificial cornea 10 is formed to be a monolithic structure, i.e., a structure having no seams or joints and preferably formed from a single blank or block of material. For example, the artificial cornea 10 may be machined from a block of suitable hydro gel polymer (when fully dehydrated to allow machining) such as the copolymer of hydroxyethyl methacrylate and methyl methacrylate as described above. The material may be machined using techniques commonly used for manufacturing intraocular lenses. Exemplary machining techniques utilize a rotary diamond lathe such as that manufactured and sold by Benz Research and Development. Once the artificial cornea 10 has been machined, it can be polished, cleaned, hydrated and sterilized for subsequent use and implantation.

Optionally, a peripheral edge 30 of the anterior surface of the center optic may be modified (or left unmodified) to support the growth of an epithelium over an annular region with a width typically in the range from 0.1 mm to 1 mm. As described in the Summary above, when the center optic material inherently inhibits the growth of the epithelium, the annular region (bounded by broken line 32) may be modified by coating or depositing an epithelial-growth promoting material. Roughening the texture of the annular region or making the annular region porous can also promote the growth of epithelium over the annular region. When the center optic material inherently promotes an epithelial layer, the anterior region of the center optic inside of broken line 32 may be coated or deposited with a material which inhibits epithelial growth, such as a silicone or methacrylate.

Typical ranges and exemplary values for the dimensions of the artificial cornea 10 are set forth in Table 1 below which refers to FIGS. 4 and 5. These dimensions are given for the artificial cornea in its fully hydrated state:

Dimension Specific Value Tolerance D 0.200 mm  ±0.050 mm Ri 7.6 mm ±0.127 mm Ro 7.7 mm ±0.127 mm Rc 0.1 mm Reference Rf 7.6 mm ±0.127 mm Of 0.05 mm  ±0.050 mm Oo 0.256 mm  ±0.050 mm α 90° ±10° Da 0.8 mm ±0.127 mm Df   8 mm ±0.254 mm Dco   4 mm ±0.127 mm Dh 5.25 mm  Reference

While the annular rim 14 preferably includes apertures such as circular holes 16, it is further desirable that at least an innermost region of the annular rim adjacent to an outer peripheral wall 22 and the center optic 12 (FIGS. 1-3) remain solid. This solid section of the rim immediately adjacent to the optic will help prevent bacterial ingress and intrusion of epithelial cells in cases where the posterior cornea behind the optic has been excised, which may be necessary when the posterior cornea is very opaque. Preferably, a width W (FIG. 3) of solid material in the range from 0.25 mm to 0.75 mm will be maintained. The apertures or other open regions of the rim will thus be disposed radially outwardly from this solid region.

In other embodiments, a rim 114 which surrounds center optic 112 may be discontinuous or may consist of material with hollow sections or a scaffold structure as shown in FIG. 8A. Other variations include a discontinuous rim 214 surrounding a center optic 212 (FIG. 8B), an annular rim 314 with oblong cutouts surrounding a center optic 312 (FIG. 8C), and a scaffold rim 414 surrounding a center optic 412 (FIG. 8D).

Referring now to FIGS. 6A through 6F, implantation of the artificial cornea 10 of the present invention into a cornea C will be described. As illustrated in FIG. 6A, the cornea C having opaque or other optically interfering regions O present, typically in its central region, is illustrated. In order to introduce the artificial cornea 10, a central region of the CR of the cornea is cut out and removed, as illustrated in FIG. 6B. Cutting may be achieved in a conventional manner, typically using a femtosecond laser, optionally combined with a mechanical trephine, to cut the cylindrical pocket in a posterior direction. In implanting an artificial cornea in accordance with the present invention, it is very important that the depth of the pocket be carefully controlled, particularly around the peripheral edge. The depth will typically be controlled at from about 200 μm to 400 μm, leaving a sufficient posterior thickness of the cornea beneath the pocket for corneas having an average thickness of 500 to 600 um. In cases of abnormally thick corneas, such as commonly found in cases of corneal edema due to endothelial failure, the depth of the pocket may be as much as 800 um to compensate for the increased thickness of the cornea. The pocket will be formed with a posterior wall PW, as shown in FIG. 6B. After the pocket P has been formed, an annular pocket AP is formed about the peripheral base of the center pocket P, as illustrated in FIG. 6C. Alternatively, a lamellar pocket, wherein the posterior wall PW and the annular pocket AP are continuous, is first be created followed by the removal of central region CR to create the anterior opening. The dimensions of the main pocket and annular pocket will be selected to be compatible with the dimensions of the artificial cornea 10 described above. For example, if the artificial cornea has the preferred dimensions set forth in Table 1, then the depth of the pocket should be 200 μm, the diameter of the pocket should be 3.5 mm, and the outer diameter of the annular pocket AP extending around the central pocket P should be 8.5 mm.

Once the central pocket P and annular pocket AP have been formed, the artificial cornea 10 can be folded or otherwise constrained, as illustrated in FIG. 6B, and inserted in a posterior direction into the central pocket P. As the artificial cornea 10 is inserted, the constraint can be released so that the annular rim 14 opens radially outwardly and enters the annular pocket AP, as illustrated in FIG. 6E. The artificial cornea 12 can then optionally be sutured in place, typically using resorbable nylon sutures. Typically, the artificial cornea of the present invention will be self retaining within the cornea even without sutures.

Alternatively, as illustrated in FIG. 6F, the artificial cornea 10 can be introduced through a lateral incision LI formed to provide access. Use of a lateral incision may be selected when, for example, the pocket maker described in commonly owned U.S. Pat. No. 7,223,275, is used for forming the pocket.

In FIG. 7A we see that the optic 112 of the Boston Artificial Cornea rises above the surface of the donor carrier cornea which will cause irritation by abrading the inner lining of the patient's eyelid. In FIG. 7B we see that optic 212 of the Alphacor resides under the surface of the cornea, which produces a divot that will accumulate mucus and debris, thus obscuring the patient's vision. In FIG. 7C the edges of the optic 12 of the artificial cornea of the present invention is at the same level as the surrounding cornea, additionally there is no gap between the surrounding corneal tissue and the optic because the opening of the cornea is sized to be slightly smaller than the optic diameter, which provides a snug fit. Also note that the angle α of the side of the optic matches the angle of the adjacent incision.

While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims. 

What is claimed is:
 1. A reversibly deformable artificial cornea comprising: a monolithic body having a diameter between 4 mm and 10 mm comprising a center optic surrounded by a rim, wherein the center optic has a diameter in the range from 3 mm to 9 mm and a optic height in the range from 200 μm to 800 μm and the rim has a width in the range from 0.5 mm to 4.5 mm and a median thickness in the range from 50 μm to 200 μm; wherein the monolithic body is comprised of a polymeric hydrogel having a Young's modulus in the range from 0.3 MPa to 100 MPa when fully hydrated.
 2. An artificial cornea as in claim 1, having a tensile strength of at least 1.5 MPa.
 3. An artificial cornea as in claim 1, having an elongation to break of at least 100%.
 4. An artificial cornea as in claim 1, wherein the optic height of the center optic varies less than ±50 μm.
 5. An artificial cornea as in claim 1, wherein an angle between the center optic and the rim varies by less than ±10°.
 6. An artificial cornea as in claim 1, wherein the rim circumscribes a posterior edge of the center optic.
 7. An artificial cornea as in claim 1, wherein at least an anterior surface of the center optic is convexly shaped to provide a refractive power generally equal to a native cornea.
 8. An artificial cornea as in claim 7, wherein a center optic provides a refractive power in the range from 30 diopter to 70 diopter when implanted in a cornea.
 9. An artificial cornea as in claim 8, wherein both the anterior and posterior surfaces of the center optic are convexly shaped.
 10. An artificial cornea as in claim 9, wherein the anterior surface is flatter than the posterior surface.
 11. An artificial cornea as in claim 1, wherein the rim has apertures to allow passage of nutrients and oxygen.
 12. An artificial cornea as in claim 11, wherein the apertures occupy from 10% to 90% of the annular area of the rim.
 13. An artificial cornea as in claim 9, wherein the apertures are round holes disposed uniformly about the annular rim.
 14. An artificial cornea as in claim 1, wherein the polymeric hydrogel comprises material selected from the group consisting of a hydrophilic acrylic material, a hydrophobic acrylic material, a silicone polymer hydrogel, a collagen polymer hydrogel, and an interpenetrating network hydrogel.
 15. An artificial cornea as in claim 1, wherein the polymer hydrogel has an oxygen permeability of at least 3 Barrer.
 16. An artificial cornea as in claim 1, wherein the polymer hydrogel comprises a material selected from the group consisting of Lotrafilcon A, Lotrafilcon B, Balafilcon A, Comfilcon A, Senofilcon A, Enfilcon A and Galyfilcon A.
 17. An artificial cornea as in claim 1, wherein an annular peripheral region of an anterior face of the center optic promotes epithelial growth while the anterior face within the annular peripheral region inhibits epithelial growth.
 18. An artificial cornea as in claim 17, wherein the annular peripheral region is covered with an epithelial growth-promoting material, is roughed, or is porous.
 19. An artificial cornea as in claim 17, wherein the anterior face of the center optic within the annular peripheral region is covered with a material that inhibits epithelial growth.
 20. A method for implanting an artificial cornea in a cornea having an impaired center region, said method comprising: forming in the cornea a central anterior opening having a posterior surface surrounded by a peripheral side wall, wherein the opening has a uniform peripheral depth in the range from 200 μm to 800 μm; and implanting an artificial cornea in the central anterior opening wherein the implant has a center optic with a peripheral wall having a uniform optic height within ±50 μm of the peripheral depth of the central anterior opening.
 21. A method as in claim 20, further comprising: forming a lamellar pocket around at least a portion of peripheral side wall of the central anterior opening; and inserting a rim circumscribing the corneal implant into the lamellar pocket to anchor the implant in the opening.
 22. A method as in claim 21, wherein the lamellar pocket is formed around the periphery of the posterior surface of the central anterior opening and the rim surrounding a posterior edge of the center optic of the corneal implant.
 23. A method as in claim 20, wherein the central anterior opening is formed to have a diameter smaller than that of the center optic, wherein the corneal tissue seals against the peripheral wall of the center optic to inhibit the ingrowth of epithelial cells, the entry of bacteria, and the loss of fluid.
 24. A method as in claim 20, wherein the implant is inserted in a posterior direction through the anterior opening
 25. A method as in claim 20, further comprising forming a lateral passage through the cornea into the central anterior opening and inserting the corneal implant through the lateral passage.
 26. A method as in claim 20, wherein the artificial cornea anchors without sutures or adhesive.
 27. A method as in claim 20, wherein a lamellar pocket is first made across the central cornea and then the central anterior opening is created over the region of the lamellar pocket. 